1. Field of the Invention
The present invention relates to a differential front axle housing used for industrial vehicles such as a fork lift or the like, and to a method of producing the same.
2. Description of the Prior Art
As is well known, a front axle housing used for a fork lift requires greater strength than these used for ordinary vehicles. This is because a support point for supporting a mast device tiltably in direction along the front and rear dimensions of the vehicle is on the axle housing. Also, in general, the front axle housing mainly comprises a differential housing and an axle tube, which are usually produced individually and then welded to each other for connection.
In view of such circumstances, conventionally, a typical differential housing for a front axle of a fork lift is formed of cast steel which is capable of withstanding a heavy load, and of being welded for connection.
FIGS. 5 and 6 show one example of conventional steel-cast differential housings used for fork lifts. A differential housing 11 has the following schematic construction, being formed in a generally cylindrical shape and laying an axis extending in direction from the front end to the rear end (from top to bottom in the plane of FIG. 5) of a vehicle (not shown). It also includes an opening 12 for connecting a differential carrier at one end along the axis, and flange portions 13 connected to an axle tube (not shown) and positioned diametrically opposite to each other on the right and left sides of the outer circumference of the differential housing 11. Furthermore, a fixing bracket and a mast pivot bracket are also fixed to the outer circumference of the axle tube for attaching the front axle housing to the body frame, though not shown in the drawings.
However, casting faults, for example, "a gas nest", might be produced in the steel-cast differential housing described above, and it is essential that such a gas nest be repaired, which further involves a thermal treatment for the repaired portion. Since the gas nest is often found during machining of metals, it has to be repaired after machining. This is extremely troublesome. Also, the cast-steel differential housing is known to produce residual stress, and a thermal treatment is required in order to eliminate it.
As stated above, the cast-steel differential housing requires not only ordinary production processes but also additional processes for readjustment purposes, thus causing extremely poor productivity.
Further, the differential housing 11 is provided with a seating face 15 in the form of a working reference surface for finishing the inner diameter of the flange portions 13 and a seat face for connection to a gear housing, and for machining tap holes 14 or the like. As is clearly seen from the dotted line in FIG. 5, a considerable amount of material has to be removed from the original seat face in order to form the targeted seat face 15, thus wasting materials. Also, the steel-cast products require a large volume of liquid metal for indirectly related production purposes, such as for the hot top and runner, the use of which is also a waste of materials.